Hermetically packaging a microelectromechanical switch and a film bulk acoustic resonator

ABSTRACT

A film bulk acoustic resonator wafer and microelectromechanical switch wafer may be combined together in face-to-face abutment with sealing material between the wafers to define individual modules. Electrical interconnects can be made between the switch and the film bulk acoustic resonator within a hermetically sealed chamber defined between the switch and the film bulk acoustic resonator.

This is a divisional of prior application Ser. No. 10/218,729, filedAug. 14, 2002 now U.S. Pat. No. 6,713,314.

BACKGROUND

This invention relates generally to microelectromechanical system (MEMS)radio frequency switches and film bulk acoustic resonator filters.

In a number of radio frequency applications, a radio frequency MEMSswitch and a film bulk acoustic resonator filter are used together.Currently, filter devices, such as film bulk acoustic resonators, arepackaged individually. If one desires to utilize a MEMS switch with suchfilter devices, an interpackage connection would be needed. As a result,a considerable amount of space on a circuit board is required tointerconnect both the switches and the individually packaged filterdevices. Interconnections between the devices must be provided that mayincrease costs as well as parasitic capacitance.

It is also relatively difficult to handle the small dies associated withthe radio frequency MEMS switch and the film bulk acoustic resonator. Itis relatively awkward to interconnect these dies and the size ofresulting structure may be considerable.

Thus, there is a need for better ways to assemble film bulk acousticresonators with microelectromechanical system radio frequency switches.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged cross-sectional view of a microelectromechanicalsystem switch in accordance with one embodiment of the presentinvention;

FIG. 2 is an enlarged cross-sectional view of a film bulk acousticresonator in accordance with one embodiment of the present invention;

FIG. 3 is an enlarged cross-sectional view of a module including theswitch of FIG. 1 and the film bulk acoustic resonator of FIG. 2 inaccordance with one embodiment of the present invention;

FIG. 4 is an enlarged cross-sectional view of the embodiment shown inFIG. 3 after further processing in accordance with one embodiment of thepresent invention;

FIG. 5 is a cross-sectional view of the embodiment shown in FIG. 3 afterfurther processing in accordance with another embodiment of the presentinvention; and

FIG. 6 is an enlarged cross-sectional view of the embodiment shown inFIG. 3 after further processing in accordance with yet anotherembodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1, a microelectromechanical system (MEMS) radiofrequency (RF) switch 11 may be formed on a substrate 10. The switch 11may include a cantilevered switch element 14 that is electrostaticallyattracted towards and away from the substrate 10 to make or breakcontact with the contact 12. In one embodiment, an electric field may beutilized to attract the cantilevered switch element 14 to make contactwith the contact 12.

Referring to FIG. 2, a film bulk acoustic resonator (FBAR) 15 inaccordance with one embodiment of the present invention may be formed ona substrate 16 with a backside cavity 24. An upper electrode 22 and alower electrode 18 may sandwich a piezoelectric film 20.

Referring to FIG. 3, the switch 11 may be assembled in an invertedconfiguration on the film bulk acoustic resonator 15 using a hermeticsealing material 26 and a conductive interconnect 28. The interconnect28 may make an electrical connection between the upper electrode 22 andthe contact 12 a and between the lower electrode 18 and the contact 12 bassociated with the switch element 14 a. In some embodiments, theinterconnect 28 material may be a metal bonding material such as asolder joint or a metal thermo-compression bonding, to mention twoexamples.

A chamber 48 may be defined between the switch 11 and the FBAR 15 usingthe hermetic sealing material 26. The material 26 may be a solder ring,frit glass ring, anodic bonding, or a plastic ring, to mention a fewexamples. Suitable plastic rings includes those made of epoxy, resin, ora polymer such as benzocyclobutene (BCB).

As a result, the switch 11 may be packaged in close proximity to theFBAR 15, reducing the interconnection length and simplifying theinterconnection process. This may result in better RF performance, fewercomponents, and a smaller footprint in some embodiments of the presentinvention. In addition, the module may have lower costs than separateswitch and filter devices. Also, the packaging may be implemented at thewafer level.

Thus, a wafer containing a large number of switches 11 and FBARs 15 maybe combined together to define individual modules 50, which aresubsequently separated from the wafer, forming, at the same time, alarge number of modules 50. In one embodiment of the present invention,one or both of the wafers, including the switches 11 and/or the FBARs15, may have the conductive interconnect material 28 formed thereonbefore combining with the other of the switch or FBAR. The conductivematerial 28 may be applied using thick resist or electroplating, as twoexamples. One or both of the wafers may also have the sealing material26 preapplied. The FBAR 15 and switch 11 may be assembled together, atthe wafer level, using an assembly tool such as a wafer bonder. In someembodiments, this assembly may be done in a dry ambient at a specifiedpressure. The cavity 24 in the backside of the FBAR 15 wafer can be madeeither before or after the wafers are assembled into the module 50. Awafer 30 may be applied over the backside cavity 24 to form the module50.

Referring to FIGS. 4 through 6, a variety of techniques may be used toform interconnects from the outside world to the switch 11 and the FBAR15. Referring to FIG. 4, a metal via 32 may be formed through the layer30 down to the upper electrode 22 and the lower electrode 20 of the FBAR15 in one embodiment of the present invention.

Alternatively, as shown in FIG. 5, metal vias 34 may be formed from thetop through the substrate 10 of the switch 11 to make electrical contactwith the contacts 12 of the switch 11.

In accordance with still another embodiment of the present invention,electrical interconnections may be made by sawing through the wafer 30and the wafer including the FBAR 15 to create the tapered shape shown inFIG. 6. The FBAR 15 may then be coated with a contact metal 36 thatmakes electrical connections to the upper and lower electrodes 22 and 18of the FBAR 15. In some embodiments, the tapered structure may be formedby sawing at the wafer level.

In one embodiment, the FBAR membrane may not be released when the switch11 and FBAR 15 wafers are bonded together. In this embodiment, the FBAR15 still needs a backside silicon etch, that may be done either using awet etch such as KOH or tetramethylammonium hydroxide (TMAH), or bybackside grinding the FBAR wafer and using a plasma etch. The packagingmay be completed afterwards by bonding the wafer 30 to the backside ofthe filter 15 wafer.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

1. A packaged electronic device comprising: a microelectromechanicalswitch including a first surface having a cantilevered switch element; afilm bulk acoustic resonator having a first surface having upper andlower electrodes and a piezoelectric film formed thereon; said switchand said resonator arranged with said first surfaces in opposition toone another; and a sealing ring between said surfaces to define achamber between said switch and said resonator.
 2. The device of claim 1including electrical contacts between said switch and said resonatorextending through said chamber.
 3. The device of claim 1 wherein saidresonator includes a cavity in a second surface of said resonator, saidcavity being covered by a substrate.
 4. The device of claim 1 includingcontacts extending from the exterior of said device through saidresonator to contact at least one of said electrodes.
 5. The device ofclaim 1 including contacts that extend from the exterior of said devicethrough said switch to make electrical contact with said switch on itsfirst surface.
 6. The device of claim 1 wherein said resonator hastapered exterior conductive surfaces that make electrical contact withsaid electrodes.
 7. A semiconductor assembly comprising: a first waferincluding a microelectromechanical switch formed thereon on a first faceof said first wafer; a second wafer with a film bulk acoustic resonatorformed on a first face of said second wafer; and said wafers connectedin first face-to-first face alignment.
 8. The assembly of claim 7including a sealing material around the first faces of said wafers todefine a hermetically sealed chamber between said wafers.
 9. Theassembly of claim 7 wherein said second wafer includes a backside cavityand a third wafer formed over said backside cavity.
 10. The assembly ofclaim 7 including a conductive contact extending between said film bulkacoustic resonator and said microelectromechanical switch.
 11. Theassembly of claim 7 further including a contact extending from theexterior of said assembly through said wafer with said film bulkacoustic resonator to make contact electrically with said film bulkacoustic resonator.
 12. The assembly of claim 7 including a contact onthe exterior of said assembly and extending through said wafer with saidmicroelectromechanical switch.
 13. The assembly of claim 7 including anotch formed in said film bulk acoustic resonator to enable electricalconnection from the outside world to said film bulk acoustic resonator.